The present invention relates to a device for detecting focusing in an optical instrument, such as a camera, which includes an objective lens and a plane, such as a light sensitive film, on which a real image of an object formed by the objective lens is intended to be focussed.
To automate the focussing in a photographic camera, various devices have been proposed for electrically detecting the focussing of a lens. It is usual that, in the objective field, a plurality of photographic objects, at different distances from a photographic camera, are disposed in various arrangements. However, a problem has been experienced in the use of these devices where the arrangements of various photographic objects in the objective field are complicated. Thus difficulties are encountered in detecting the proper focussing of a lens for a specific photographic object selected by the photographer from among those various photographic objects.
In U.S. Pat. No. 3,543,666, there is disclosed a means by which focus is detected through measurement of the convergance of the photographer's eyes. This however, relates to a pair of eyes of the photographer.